We use scope statement for ensuring about the assumptions and constraints ( double checking). We are not worried about wbs and wbs dictionary now as those are captured by our Activities.

This is how I remembered.

I am asking my team members to do the estimation of activity duration , I will give them the activities and in order to cross check i will give them scope statement so they know what is included not included also what are the assumptions and constraints. I don't have to burden them with scope baseline ( think about having 10 people to go through all these documents just to get the assumptions and constraints verification ( this is my way of remembering ).

So what is optimal for a person to do their work of estimating in less time that is what we have to give. if you provide scope baseline also it will work as scope statement is included in scope baseline. Hope this helps.